This invention relates to a magnetic storage medium for use in a magnetic storage or memory such as a magnetic disk unit or a magnetic drum unit.
In magnetic storage means having a read/write head (hereinafter simply called a head) and a movable magnetic storage medium represented by a magnetic disk, a prevailing mode of reading and writing information is the so-called contact-start-stop (CSS) method. According to this method, the head is in contact with the magnetic surface of the storage medium at the start of a read or write operation. Starting the operation the magnetic storage medium is driven to turn at a given rate and to provide a narrow spacing or air bearing between the head and the magnetic surface of the storage medium, and in that state the operation is conducted. At the end of the operation the storage medium stops turning and again comes into contact with the head which is held under a predetermined load. Therefore, friction force acts on both the head and the storage medium so that the head and/or the storage medium undergo gradual wear, which sometimes results in scratching of the head and/or the storage medium. Besides, in some cases a slight change in the orientation of the head in the friction contact state becomes a cause of uneven distribution of the load on the head and, consequently, scratching of the head and/or the storage medium. As another problem, the head and the magnetic storage medium tend to stick to each other when long left in contact with each other and, then, they do not smoothly part from each other at the start of a read or write operation.
To protect the magnetic storage medium from being scratched or otherwise damaged and also to prevent it from sticking to the head, it is usual to provide a lubricating coating on the magnetic surface of the storage medium. For this purpose various kinds of lubricative materials have been proposed. For example, Japanese patent application provisional publication No. 52-49805 (1977) shows several kinds of side-chain and straight-chain perfluoroalkyl polyethers represented by the following formulas. ##STR1##
However, the lubricants thus far proposed are not yet fully satisfactory because the lubricant layer formed of any of such lubricants is gradually removed as the CSS operation is repeated many times and fails to prevent scratching of the magnetic storage medium while it is desired to further repeat CSS operations on that storage medium. Besides, the removed lubricant tends to locally accumulate on the sliding contact surface to a undesirably large thickness, and this phenomenon becomes a cause of sticking of the magnetic storage medium to the head.